Ion engine thrust multiplier



I Nov. 3, 1970 P. MAHADEVAN ETAL I0N ENGINE THRUST MULTIPLIER Filed Jan. 22, 1968 2 Sheets-Sheet 1 o \\\\J I i 12 v i I I CONVENTIONAL I s I I 7 ENGINE I D a E i I y p i L 1 H 32 j 5 IO ,b q A l, ,bk :0 A a, y 3 3.*,,;.,,.: I

I I- I P I l I- AVI hi Avg F AV3 Pi AV4 J" I* i' V| V2 V3 V4 FIG I CHARGE CHARGE CHARGE CHARGE CHARGE TRANSFER A TRANSFER B TRANSFER C TRANSFER D TRANSFER E IN GAS IN GAS IN GAS IN GAS IN GAS IA v 1 c VACUUM ELECTRIC I9 FIELD 0 -v -v -v v -V POTENTIAL I 2 3 v 4 5 INVENTOR.

F IG, 2 'PARAMESwAR MAHADEVAN GUSTAV D. MAGNUSON ATTORNEY Ndv. 3, 1970 1 P. MAHADEVAN ETAL ION ENGINE THRUST MULTIPLIER Filed Jan, 22, 1968 2 Sheets-Sheet 2 H I] I' FIG-.3 T

INVENTOR PARAMESWAR MAHADEVAN GUSTAVD. MAGNUSON BY 22mm TON ATTORNEY United States Patent 'ce 3,537,266 ION ENGINE THRUST MULTIPLIER Parameswar Mahadevan, Cerritos, Calif., and Carl E. Carlston and Gustav D. Magnuson, Charlottesville, Va., assignors to General Dynamics Corporation (Convair Division), San Diego, Calif., a corporation of Delaware Filed Jan. 22, 1968, Ser. No. 699,574 Int. Cl. F03h 5/00; H05h 5 06 U.S. Cl. 60-202 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The most common method of producing thrust for electrostatic propulsion is an ion engine that ejects positive ions of elements, such as mercury, cesium, or highly charged colloidal particles at predetermined velocities of efllux. In order to maintain electrical neutrality of the space vehicle, the method now favored is to bleed into the intense positive ion jet a stream of electrons at appropriate densities from an electron emitter. Charge exchange processes between the positive ion beam and a neutral gaseous target have also been proposed to provide neutralization of the ion beam. While such ion engines have shown considerable promise for use as space thrust producing engines, it is of advantage to multiply the output thrust of such engines and to provide a neutral atom output that requires a minimum or no neutralization of the ion beam.

Thus, this invention is capable of providing an intense beam of electrically neutral particles for space propulsion, which beam magnifies several times the thrust available from a conventional ion engine, and is capable of varying the average velocity of the electrically neutral particles in flight by an appropriate control means.

SUMMARY OF THE INVENTION The ion engine thrust multiplier of our invention comprises an environmental chamber or container for magnifying the thrust available from a conventional ion engine. The ion streams from a conventional ion engine, where positive ions are generated from a given species of gas, into the environmental chamber. As the positive ions from the ion source or conventional ion engine enter the chamber, they collide inelastically with particles of a gas of the same species maintained at a desired pressure. These collisions create neutral atoms and relatively slow moving positive product ions. The fast moving neutral atoms travel in the original direction of the input ion beam and at substantially the same speed. The chamber has successive stages of a uniformly increasing electrical field and the positive product ions are drawn in the same direction by the uniform field. The stages of the electrostatic field accelerate the slow moving positive product ions to a speed approaching the speed of the input ions. The product ions in another collision transfer their charge to the parent gas atoms after traversing appropriate path lengths. While the neutral atom beam is attenuated to a slight degree by elastic and inelastic collisions in its 3,537,266 Patented Nov. 3, 1970 passage through the gas in the environmental chamber, at kinetic energies of the order of kev. the angular deviation of the neutral atom beam due to these collisions is negligibly small. Through the various stages of charge transfer reactions and re-acceleration of the created slow moving positive product ions, the number of fast moving neutral atoms formed in the primary and sucessive charge transfer reactions are substantially increased to multiply the thrust available from the ion stream source.

In principle of operation, an intense collimated heavy ion beam, such as developed from mercury, cesium, argon, or any other suitable gas, issues out of a conventional ion engine. The positive ion beams pass into the charge transfer chamber of this invention containing the same species of gas at optimum pressure, and in a uniform electrostatic or electrical field. The positive ions in the beam exchange charge with the thermal gas atoms in inelastic collisions and in resultant symmetrical resonant reactions forming fast neutral atoms and slow positive ions. The reactions are generally as follows.

The fast neutral atoms formed retain the same original velocity as the ions, are unchanged in direction and are unaffected by the electrostatic field. The slow moving product ions are accelerated in even stages to again collide and transfer their charge. This cascading process of acceleration of the slow moving positive ions to the desired velocity followed by charge transfers that create an increasing number of fast neutral atoms is repeated several times. Each charge transfer stage thus constitutes a stage of flux and thrust magnification for the ion engine.

The thrust magnification of an ion stream provided by this invention is very advantageous for use in space missions for several reasons. The average velocity of the emerging neutral beam is normally less than that of the original ion beam from the ion engine. So it is possible to obtain variable specific impulse thrust from proper variations of the engine parameters such as variations in field potentials and potential gradients in the charge transfer stages of the charge transfer chamber. Also Where low specific impulse thrust is required, as for example where an ion engine has to be run in space at far from optimum operating conditions resulting in loss of thrust, these undesirable features of low impulse operation can be compensated for by the successive charge transfer multiplication of our invention.

Thus it is an object of this invention to provide a new and improved neutral atom propulsion engine.

It is another object of this invention to provide a new and improved ion engine thrust multiplier.

It is another object of this invention to provide a new and improved intense beam of electrically neutral particles for space propulsion.

It is another object of this invention to provide a new and improved means for multiplying the thrust available from a conventional ion engine by successive charge transfer.

Other objects and many intended advantages of our invention will become more apparent in reading the following detailed description and examining the drawings in which:

FIG. 1 is a cross-sectional side view and schematic representation of an embodiment of our invention.

FIG. 2 is a schematic representation of the charge transfer that takes place in the operation of our invention.

FIG. 3 is a cross-sectional view and perspective view M the positive ion 61 and a second positive ion 64. The neutral atom 66 travels'in the same direction 'orinove of the embodiment of our invention asg'eiierally'illu's trated in FIG. 1.

I Referring now to .FIGS. 1 and 3, a conventional ion engine or ion source 10 provides a plurality of intense, collimated, heavy, positive, ion beams 11. These posi: tive ionbeams issuing out of the ion engine 10 are generally created from gaseous mercury, cesium, argon or other suitable elements or materials; The ion streams pass through appropriately aligned apertures 42 and 44 in a plurality of charge plates that are positioned 'along the length of a charge transfer chamber 9. The charge transfer chamber 9 comprises an outer cylindrically shaped housing 20 of insulating material having a plurality of insulating spacers 21 positioned against or secured to the inner surface of the housing 20. The apertured plates, as for example plates 17, 18 and 19, are appropriately spaced and held by the insulating spacers 21 within the charge transfer chamber 9. As may be seen, the apertured plates are grouped into, for example, groups 17 and 18 forming drift regions A, B, C, D, and E and acceleration regions 46. A plurality of potential sources V1, V2, V3, V4, and V provide appropriate potentials to certain groups of charge plates. As for example, potential source .V1 or 15 is connected across the charge plates 17 and 19.'A second potential source AVI or 14 is connected through lines 34 and 36 to ment as the positive ion 61" and thus passes out of the charge transfer chamber 9. The second positive ion 64 drifts and is accelerated by virtue of the electrostatic field in the charged transfer stage A'to a--,velocity approaching the velocity of the input-positive ion 61.- The second positive ion 64 impacts at point 68, with another atom of the species gas again providing a charge transfer and creating a second neutral atom 70 and a third-'positive ion 72. As may be seen this multiplication continues in the successive stages of the charge transfer stages A, B, C, D, and E to provide the increased'multiple beam 12 that is emitted from the charge transfer chamber 9.

different groupings of charge plates 18 and 19. A similar connection of potentials are connected through appropriate lines, as for example lines 38 and 40, for connecting AVZ to the next adjacent charge plates and similar electrical connections connect AV3, AV4, and AVS, to

to respective adjacent charge plates. Accordingly, the 7 A gas of the same species as used in the conventional ion engine 10 is injected through apertures 32 and through the insulating sheath 20 to the respective spaces A, B, C, D, and E of the charge transfer chamber 9. Referring to FIG. 3, the gas vapor is obtained from a suitable boiler (not shown) which contains the material vaporized, and is transported through a line to a manifold 75 and is distributed through the plurality of distributing conduits 29 supplying gas to the charge transfer chamber 9. The charge transfer chamber 9 is surrounded by a source of heat provided by any suitable means, such as electrical heating members 24 embedded in an insulated body 23 that is positioned on the outer surface of the insulating sheath 20. The small amount of heat provided by the heating device 24 supplements the heat input from the ion thruster or engine 10 to prevent condensation of the propellant vapor and maintains the. proper pressure for thrust multiplication. It should be understood that the spacings between, for example plates 18 and 19 or between plates 17 and 18, and the pressure of the propellant gas species in the environmental chamber 9 are selectively adjusted for a specific application,

The apertures 42 and 44 in the charge plates, as fo example charge plates 17, 18, 19 and 30 are aligned with discharge openings in the output plate of the ion engine 10 so that the ion streams 11 pass directly in linear movement through the apertures in the charge plates and out the discharge of the charge transfer chamber 9. V Referring to FIGQ2, there is illustrated the operation of the charge transfer chamber 9 in multiplying the propellent beam. An ion beam 11 passes through openings 42 in the charge plates 60. A positive ion 61, for example, enters into the first charge transfer stage A and impacts with an atom of, the species gas at point 62.

This inelastic collision provides a charge transfer that creates the neutral atom 66 having the same velocity as Accordingly, the total flux leaving the device from each aperture is in this way greater than the incoming flux. The number-.of stages may be increased or decreased for optimum operation for a specific space propulsion 'ob'-. jective. In general, the voltage V1 will be the same as the accelerating voltage of the original incoming ions 11. The distances between plates, for example, is determined by the species gas used and the energy spread desired of the existing flux.

It should be recognized in referring to FIG. 1, that the slow ions drift in spaces A through E and accelerate in the spaces 46. However the plates 17 and 18 can be combined to provide a single potential region wherein the ions are accelerated in as well asdrawn through the regions A, B, C, D, and E.

While the primary output in beam 12 comprises neutral fast moving atoms that do not create a space charge, there are a few positive ion products resulting from the charge transfer process that also leave the output of the chamber 9. Accordingly, when the slow, positive, product ions leave the chamber 9, they createa. space charge that may require neutralizing. Accordingly a known space charge neutralizer 13 functions to neutralize this space charge by supplying electrons that neutralize the positive product ions. The space charge neutralizer is normally used only when positive ions are issued from the final stage, and can be any of the presently existing space charge neutralizers already in standard use on ion thrusters. The charge transfer chamber 9 will normally be secured to the discharge end of the conventional ion engine 10 and may be held' together and against the conventional ion engine by appropriate straps and longitudinal connectors 26 in the manner known in the art. An insulating member 24 is positioned at the discharge end of the multiplying device 9 to provide an insulating connectio for the connectors 26.

While many features and applications of our invention have been disclosed in the specific embodiment, it should be recognized that other possible configurations, uses and adaptations of our invention are possible by those skilled in the art.

Having disclosed our invention, we now claim:

1. An ion engine thrust multiplier comprising: ion source means for providing at least one ion stream, multiplier means for increasing the thrust of said ion stream by successive charge transfer between positive ions, and gas atoms providing an increased output of neutral atoms and second positive ions, said multiplier means includes'a charge transfer cham her that receives said ion stream, 1 said chamber has a plurality of grouped and spaced pairs of electrically energized charge plate means positioned in and spaced along the length of said chamber for providing separate successive stages 'of auniform electrostatic field in the direction of movement of said ion stream, each of said pairs of plate means comprises-a pair of plates for receiving a given voltage differential between the plates,

5 said second positive ions being accelerated between said pairs of plates, and gas source means for uniform injection of gas atoms into said chamber in spaces between said pairs of plates along the length of said chamber. 2. An ion engine thrust multiplier as claimed in claim 1 in which:

said ion source means provides a plurality of culminated positive ion streams, and each of said plurality of charge plates have a plurality of openings that are aligned to receive said ion streams and pass said created neutral atoms and said second positive ions. 3. An ion engine thrust multiplier as claimed in claim 2 including:

means surrounding said chamber for providing sufiicient heat to said chamber to substantially prevent condensation of said gas and maintain proper pressure in said chamber for thrust multiplication.

References Cited UNITED STATES PATENTS 3,136,908 6/1964 Weinman 313-63 3,156,090 11/1964 Kaufman 60202 2,253,402 5/1966 Hammer n 60202 3,380,249 4/1968 Meckel 60-202 CARLTON R. CROYLE, Primary Examiner.

US. Cl. X.R-. 

